Re: [PATCH -next v2 7/7] md/raid1-10: limit the number of plugged bio

[Yu Kuai]

Hi,

在 2023/05/29 10:08, Xiao Ni 写道:
> Hi Kuai
>
> There is a limitation of the memory in your test. But for most
> situations, customers should not set this. Can this change introduce a
> performance regression against other situations?

Noted that this limitation is just to triggered writeback as soon as
possible in the test, and it's 100% sure real situations can trigger
dirty pages write back asynchronously and continue to produce new dirty
pages.

If a lot of bio is not plugged, then it's the same as before; if a lot
of bio is plugged, noted that before this patchset, these bio will spent
quite a long time in plug, and hence I think performance should be
better.

Thanks,
Kuai
> Best Regards
> Xiao
>
> On Wed, Apr 26, 2023 at 4:24 PM Yu Kuai <yukuai1@xxxxxxxxxxxxxxx> wrote:
> > From: Yu Kuai <yukuai3@xxxxxxxxxx>
> >
> > bio can be added to plug infinitely, and following writeback test can
> > trigger huge amount of plugged bio:
> >
> > Test script:
> > modprobe brd rd_nr=4 rd_size=10485760
> > mdadm -CR /dev/md0 -l10 -n4 /dev/ram[0123] --assume-clean
> > echo 0 > /proc/sys/vm/dirty_background_ratio
> > echo 60 > /proc/sys/vm/dirty_ratio
> > fio -filename=/dev/md0 -ioengine=libaio -rw=write -bs=4k -numjobs=1 -iodepth=128 -name=test
> >
> > Test result:
> > Monitor /sys/block/md0/inflight will found that inflight keep increasing
> > until fio finish writing, after running for about 2 minutes:
> >
> > [root@fedora ~]# cat /sys/block/md0/inflight
> >         0  4474191
> >
> > Fix the problem by limiting the number of plugged bio based on the number
> > of copies for original bio.
> >
> > Signed-off-by: Yu Kuai <yukuai3@xxxxxxxxxx>
> > ---
> >   drivers/md/raid1-10.c | 9 ++++++++-
> >   drivers/md/raid1.c    | 2 +-
> >   drivers/md/raid10.c   | 2 +-
> >   3 files changed, 10 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/md/raid1-10.c b/drivers/md/raid1-10.c
> > index 98d678b7df3f..35fb80aa37aa 100644
> > --- a/drivers/md/raid1-10.c
> > +++ b/drivers/md/raid1-10.c
> > @@ -21,6 +21,7 @@
> >   #define IO_MADE_GOOD ((struct bio *)2)
> >
> >   #define BIO_SPECIAL(bio) ((unsigned long)bio <= 2)
> > +#define MAX_PLUG_BIO 32
> >
> >   /* for managing resync I/O pages */
> >   struct resync_pages {
> > @@ -31,6 +32,7 @@ struct resync_pages {
> >   struct raid1_plug_cb {
> >          struct blk_plug_cb      cb;
> >          struct bio_list         pending;
> > +       unsigned int            count;
> >   };
> >
> >   static void rbio_pool_free(void *rbio, void *data)
> > @@ -127,7 +129,7 @@ static inline void md_submit_write(struct bio *bio)
> >   }
> >
> >   static inline bool md_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
> > -                                     blk_plug_cb_fn unplug)
> > +                                     blk_plug_cb_fn unplug, int copies)
> >   {
> >          struct raid1_plug_cb *plug = NULL;
> >          struct blk_plug_cb *cb;
> > @@ -147,6 +149,11 @@ static inline bool md_add_bio_to_plug(struct mddev *mddev, struct bio *bio,
> >
> >          plug = container_of(cb, struct raid1_plug_cb, cb);
> >          bio_list_add(&plug->pending, bio);
> > +       if (++plug->count / MAX_PLUG_BIO >= copies) {
> > +               list_del(&cb->list);
> > +               cb->callback(cb, false);
> > +       }
> > +
> >
> >          return true;
> >   }
> > diff --git a/drivers/md/raid1.c b/drivers/md/raid1.c
> > index 639e09cecf01..c6066408a913 100644
> > --- a/drivers/md/raid1.c
> > +++ b/drivers/md/raid1.c
> > @@ -1562,7 +1562,7 @@ static void raid1_write_request(struct mddev *mddev, struct bio *bio,
> >                                                r1_bio->sector);
> >                  /* flush_pending_writes() needs access to the rdev so...*/
> >                  mbio->bi_bdev = (void *)rdev;
> > -               if (!md_add_bio_to_plug(mddev, mbio, raid1_unplug)) {
> > +               if (!md_add_bio_to_plug(mddev, mbio, raid1_unplug, disks)) {
> >                          spin_lock_irqsave(&conf->device_lock, flags);
> >                          bio_list_add(&conf->pending_bio_list, mbio);
> >                          spin_unlock_irqrestore(&conf->device_lock, flags);
> > diff --git a/drivers/md/raid10.c b/drivers/md/raid10.c
> > index bd9e655ca408..7135cfaf75db 100644
> > --- a/drivers/md/raid10.c
> > +++ b/drivers/md/raid10.c
> > @@ -1306,7 +1306,7 @@ static void raid10_write_one_disk(struct mddev *mddev, struct r10bio *r10_bio,
> >
> >          atomic_inc(&r10_bio->remaining);
> >
> > -       if (!md_add_bio_to_plug(mddev, mbio, raid10_unplug)) {
> > +       if (!md_add_bio_to_plug(mddev, mbio, raid10_unplug, conf->copies)) {
> >                  spin_lock_irqsave(&conf->device_lock, flags);
> >                  bio_list_add(&conf->pending_bio_list, mbio);
> >                  spin_unlock_irqrestore(&conf->device_lock, flags);
> > --
> > 2.39.2
>
> .